This invention relates to a tool calibration system including a tool calibration fixture and a tool height and offset calibration insert for calibrating the position of a tool bit in a micromachining tool system. The tool calibration system was designed for use with the micromachining tool system disclosed and claimed in Omega-X Micromachining System, U.S. Application Ser. No. 750,317 and now U.S. Pat. No. 4,083,272 by Donald Miller, filed Dec. 14, 1976. This micromachining tool system is used to produce optical quality surface finishes on large sperical, asperical, flat, and irregular surfaces.
Conventional fine machining systems often resemble "T" bed turning and boring machines. Such machines often have stacked slides and may have a machine spindle mounted on one slide and a cutting tool on another slide, making a 90 degree angle with the first slide. The slides are usually quite massive and require ball-screw mechanisms for accurate movement. It is also common practice to employ caged roller mechanisms between sliding members and way surfaces to reduce friction; these devices create mechanical noise which is reflected in the surface of the workpiece. These disadvantages are avoided by the omega-X micro-machining tool system.
Several additional problems arise when a surface must be finished to an optical quality, i.e., 3 nanometers RMS (3 .times. 10.sup.-9 meter). First, the cutting tool is moved directly toward or away from the workpiece; because of the orthogonal axes and relatively large pulse increments from the pulsed motor system commanding movement of the carriage, the movements toward or away from the workpiece are large compared to the accuracy desired. Second, the inertia of the moving carriage is large; it tends to cause overtravel because the inertia is difficult to overcome before the carriage has exceeded the commanded distance. Third, the ball-screw mechanism used to move the carriage is not "stiff" enough to control the carriage movement; the mechanism is subject to backlash and dimensional changes due to stress imposed by loads. Fourth, unwanted motion can be transmitted to the workpiece from the driver through the spindle which further disturbs the desired spatial relationship of the tool to the workpiece. These errors are, of course, in addition to errors in the shape and dimensions of the tool bit employed, and errors incurred in establishing a precisely known position of the tool bit nose in relation to the workpiece.